The present invention relates to fiber optic power control devices and systems for controlling optical energy transmitted through a fiber optic. As one example, a fiber optic power control device in accordance with the present invention may comprise a controllable attenuator and attenuation system for attenuating optical energy transmitted through the fiber optic.
Fiber optic systems often require precise control of optical signal levels entering various system components. This is particularly true for systems at test and characterization stages of deployment. A controllable optical attenuator can be used, for example, to characterize and optimize the optoelectronic response of high-speed photoreceivers, wherein the detection responsivity is dependent on the average optical power incident on the photodiode.
The majority of controllable fiber optic attenuators currently commercially available rely on thin-film absorption filters, which require breaking the fiber and placing the filters in-line. Controllable attenuation is then achieved mechanically by, for example, rotating or sliding the filter to change the optical path length within the absorptive material. This adversely impacts the response speed of the device, the overall mechanical stability, zero attenuation insertion loss and optical back reflection. In general, broken fiber designs suffer numerous disadvantages such as high insertion loss, significant back reflection, and large size. These factors can be minimized, although such corrective measures typically result in added cost and/or size.
Additional issues have impeded the development of thermo-optic variable attenuators, including: (i) the thermal mass of surrounding materials and/or structures which significantly degrade device response time; and (ii) spectrally non-uniform attenuation, resulting from a dispersion mis-match between the optical mode index of the underlying transmission media and a controllable overlay material.
As described in many of the above-noted, commonly assigned, United States patent applications, techniques have been proposed to overcome these weaknesses by providing a xe2x80x9cblocklessxe2x80x9d attenuator implementation. The xe2x80x9cblocklessxe2x80x9d technique of suspending a portion of a fiber optic within a dispersion-controlled, controllable material, addresses the thermal mass responsivity and spectral uniformity problems. The portion of the fiber optic is modified to allow extraction of optical energy therefrom by the controllable material.
Now, enhanced control systems and methods for such an attenuator device, or other fiber optic power control device, are desirable to improve operability, predictability and marketability of the device. The present invention is direction to providing such enhanced control systems and methods.
The shortcomings of the prior approaches are overcome, and additional advantages are provided, by the present invention, which in one aspect relates to an attenuation system for attenuating optical energy transmitted through a fiber optic. The attenuation system includes a controllable attenuator and a control circuit coupled to the controllable attenuator. The attenuator is arranged with respect to a portion of the fiber optic, which has a side surface through which at least some of the optical energy can be controllably extracted. A controllable material is formed over the side surface for controlling an amount of optical energy extracted from the fiber optic according to a changeable stimulus applied to the controllable material, which affects the index of a refraction thereof. The control circuit controls a value of the changeable stimulus applied to the controllable material in accordance with a digitized feedback signal having a value related to the level of at least a portion of the optical energy transmitted within the fiber optic. The control circuit includes a digital filter for filtering an error signal produced by the control circuit. The error signal is produced by comparing the feedback signal to a desired reference level.
In another aspect, the present invention relates to a control system for controlling optical energy transmitted through a fiber optic. The control system includes a fiber optic power control device, arranged with respect to a portion of the fiber optic, and at least one sensor coupled to the fiber optic or the power control device for sensing the level of at least a portion of the optical energy transmitted within the fiber optic, and for outputting based thereon, a sensed level stimulus. A controller circuit is also provided and coupled to the at least one sensor for receiving the sensed level stimulus output therefrom, and coupled to the fiber optic power control device for providing a digitized feedback signal thereto. The digitized feedback signal has a value related to the sensed level stimulus. The controller circuit includes: memory for holding at least one of a control program, a control setting or a control mode to be used by the controller circuit; an analog-to-digital converter for receiving the sensed level stimulus and for converting the sensed level stimulus to a digital signal for processing within the controller circuit; a digital communication interface for facilitating monitoring of one or more of the fiber optic, the fiber optic power control device or the controller circuit, and/or for facilitating inputting or adjusting of control parameters employed by the controller circuit; and a processor for software processing of the digital signal output by the analog-to-digital converter in accordance with at least one of the control program, the control parameters or the control mode.
In still another aspect, the present invention discloses a method of controlling optical energy transmitted through a fiber optic. The method includes: disposing a fiber optic power control device with respect to a portion of the fiber optic so as to control the power transmitted therethrough, wherein the fiber optic power control device operates in accordance with one of multiple control modes; and controlling the fiber optic power control device, the controlling including automatically switching control of the fiber optic power control device from a first control mode to a second control mode of the multiple control modes, the automatic switching being responsive to detection of a defined condition of the fiber optic, the optical energy transmitted therethrough, or with the fiber optic power control device.
In a further aspect, the present invention provides a method for powering up or resetting a digital power control system which controls optical energy transmitted through a fiber optic. The method includes providing non-volatile memory for storing mode and setpoint data employed by the digital power control system; and responsive to powering up or resetting of the digital power control system, automatically reading the mode and setpoint data from the non-volatile memory and using the mode and setpoint data to initiate a control algorithm within the digital power control system for controlling optical energy transmitted through the fiber optic.
Additional features and advantages are realized through the techniques of the present invention. Other embodiments and aspects of the invention are described in detail herein and are considered a part of the claimed invention.